The present invention relates to odorizing natural gas in general and, more in particular, to the odorizing of natural gas in its liquid form.
Storage of natural gas in its liquid form is becoming increasingly common. Typically, liquid natural gas is drawn from a liquid natural gas storage vessel and vaporized outside the vessel before it is used. Obviously, at least the vaporized natural gas should be odorized for leak detection purposes.
It has long been known that ethyl and methyl mercaptans are effective odorants for natural gas. Only a very small amount of mercaptan is necessary to effectively odorize natural gas. For example, with methyl mercaptan 0.06 to 0.1 grains per 100 SCF of natural gas is sufficient to warn of natural gas leaks. However, the odorant is extremely pungent and unpleasant in concentrations above that required to warn of gas leaks.
Consequently, it is highly desirable to use only as much mercaptan as is necessary to warn of the presence of an excessive amount of gas and to definitely avoid over-odorization.
Both ethyl and methyl mercaptans freeze at a temperature which is quite a bit higher than the boiling point of liquid natural gas. This has presented a problem in odorizing liquid natural gas.
The problem is that frozen mercaptan does not dissolve fast enough to effectively odorize the liquid natural gas. As a consequence it has proven difficult in the past to effectively odorize liquid natural gas.
With the increasing demand for stored liquid natural gas, for example, in liquid natural gas-powered motor vehicles, the problem of effective odorization of liquid natural gas becomes acute.